Medical device with tail(s) for assisting flow of urine

ABSTRACT

A ureteral stent for assisting movement of urine along a patient&#39;s ureter and into the patient&#39;s bladder. The stent includes an elongated tubular segment extending toward the bladder from a kidney end region for placement in the renal cavity to a bladder end region. A central lumen connects at least one opening at the first end region to at least one opening in the bladder end region. Thin flexible tail(s) are attached to the bladder end region of the tubular segment at a point outside the bladder so as to receive urine from the opening in the bladder end region of the tubular segment and to transport urine from there across the ureter/bladder junction and into the bladder. The tails include an elongated external urine-transport surface sized and configured to transport urine along the ureter. The urine transporting surface(s) are sized and configured to extend along at least part of the ureter, across the ureter/bladder junction, and from there into the bladder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is entitled under 35 U.S.C. § 119(e)(1) to the filingdates of earlier co-pending provisional applications U.S. Ser. No.60/006,259, filed Nov. 7, 1995, U.S. Ser. No. 60/009,983 filed Jan. 16,1996, and U.S. Ser. No. 60/025,284, filed Sep. 19, 1996.

FIELD OF THE INVENTION

This application relates to ureteral stents.

BACKGROUND OF THE INVENTION

Ureteral stents are used to assist urinary drainage from the kidney tothe bladder in patients with ureteral obstruction or injury, or toprotect the integrity of the ureter in a variety of surgicalmanipulations. More specifically, stents may be used to treat or avoidureter obstructions (such as ureteral stones or ureteral tumors) whichdisrupt the flow of urine from the kidneys to the bladder. Seriousobstructions may cause urine to back up into the kidneys, threateningrenal function. Ureteral stents may also be used after endoscopicinspection of the ureter.

Ureteral stents typically are tubular in shape, terminating in twoopposing ends: a kidney (upper) end and a bladder (lower) end. The endsmay be coiled in a pigtail or J-shape to prevent the upward or downwardmigration of the stent, e.g., with physiological movements. The kidneycoil is designed to retain the stent within the renal pelvis of thekidney and to prevent stent migration down the ureter. The bladder coilsits in the bladder and is designed to prevent stent migration upwardstoward the kidney. The bladder coil is also used to aid in retrieval andremoval of the stent.

Ureteral stents, particularly the portion positioned in the ureter nearthe bladder and inside the bladder, may produce adverse effectsincluding blood in the urine, a continual urge to urinate, strangury,and flank pain accompanying reflux of urine up the stent (e.g., whenvoiding) as pressure within the bladder is transmitted to the kidney. Inshort, stents may cause or contribute to significant patient discomfortand serious medical problems.

FIG. 10 is a schematic drawing of the human urinary tract without astent, showing the renal pelvis, the kidney, the ureter, and theureteral orifices opening into the bladder. FIG. 11 depicts a typicaldouble-J stent 10 which comprises a small tube 12 which sits inside theurinary system and assists the flow of urine from the kidney (renalpelvis) to the bladder. FIG. 12 depicts prior art indwelling ureteralstent 10 in position. Such stents are typically made of biocompatibleplastic, coated plastic, or silicone material. Tube 12 typically variesin size from 4-8 fr. (mm in circumference), and it has multiple smallholes throughout its length. A coiled shape pre-formed at each end 14and 16 is designed to confine its movement within the urinary system, sothat it will be maintained in the desired position. The upper (kidney)end 14 of the stent may be closed or tapered, depending on the method ofinsertion (e.g., the use of a guidewire). The tubular stent extendsthrough the ureteral orifice 18 a and into the bladder, fixing orifice18 a open, and thereby enhancing the opportunity for reflux. Forclarity, the ureter entering bladder 20 through orifice 18 b is notshown. A monofilament thread 22 may be attached to the bladder end ofthe stent for removal, usually without cystoendoscopy.

U.S. Pat. No. 4,531,933 (“the '933 patent”) discloses a ureteral stenthaving helical coils at each end which are provided for preventingmigration and expulsion.

SUMMARY OF THE INVENTION

We have discovered a ureteral stent design that avoids patientdiscomfort and urine reflux upward toward the kidney. Rather than relyon a tubular structure to contain and facilitate all (or, in someembodiments, any) urine flow along the ureter, the invention features athin flexible elongated tail member having an elongated externalurine-transport surface. Urine flows along the outside surface of thestructure, between that surface and the inside wall of the ureter.Without limiting ourselves to a specific mechanism, it appears thaturine may remain attached to, and flow along, the external urinetransport surface. The use of a foreign body that is as small aspossible in the lower (bladder) end of the ureter and in the bladderitself decreases patient discomfort. Typically, the external urinetransport surface is sized and configured to extend along at least partof the ureter near the bladder, across the ureter/bladder junction, andfrom there through the ureteral opening into the bladder.

While most or all of the length of the stent may rely on such anexternal surface to assist flow, more typically the stent will alsoinclude an upper elongated tubular segment to transport urine along asignificant portion of the upper ureter. The upper tubular segment isconnected at its lower end to an elongated tail which has the abovedescribed external urine-transport surface. The upper tubular segmentcomprises: a) an upper region having at least a first opening; b) alower region having at least a second opening to be positioned in theureter outside the bladder, and c) a central lumen connecting the firstopening to the second opening. The elongated tail is a thin flexibletail member or filament(s) extending from the lower region of thetubular segment at a point outside the bladder so as to receive urinefrom the second opening of the tubular segment and to transport urinealong the ureter from the lower region of the tubular segment across theureter/bladder junction and into the bladder. Typically, but notexclusively, the upper region of the tubular segment is configured andsized for placement in the renal cavity.

Typically the elongated tail member comprises at least one (and morepreferably at least two) thread filament(s). Two or more of thefilaments may be configured in at least one filament loop, and,advantageously, the tail comprises no unlooped filaments, so that thetail is free from loose ends. The loop(s) can be made by joining theends of a single filament, in which case the filament loop comprises ajunction of individual filament ends, which junction typically ispositioned at the point where tail joins to the elongated tubularsegment. Preferably, the tail is long enough to effectively preventmigration of the entire tail into the ureter, and the tail has a smallerouter diameter than the outer diameter of the tubular segment.

The tubular stent segment is stiff enough to avoid crimping duringinsertion through the ureter, so that it can be inserted by typicalprocedures. The tail, on the other hand, is extremely flexible (soft) incomparison to the tubular segment, and it has a much smaller diameterthan the tubular segment to avoid discomfort. Even quite thin structureswill provide urine transport, and the thinner and more flexible the tailis, the less likely it is to cause patient discomfort. On the otherhand, the tail (and its connection to the rest of the stent) should havesufficient strength so the stent can be retrieved by locating the tailin the bladder and pulling on the tail to retrieve the stent from thekidney and ureter. Details of the tail size are discussed below. The useof reinforcing materials (e.g., sutures as described below) permits theuse of thinner tails while still providing the ability to locate thetail in the bladder and to retrieve the stent. The tail may be a suture,and the suture may be coated to avoid encrusting.

The external urine-transport surface of the tail can be convex (circularor oval in section), concave or flat. The tail filament may be fluted.The tail may, but need not, include an accurately shaped anchor segmentto control migration up the ureter. The tail may be either solid orhollow; even when hollow, it is not designed to transport a significantamount of urine internally. The tail may also be tapered.

The upper region of the tubular segment may have a portion designed forplacement in the renal cavity, which portion has enlarged diameterand/or straight sides and corners. The stent may include an extractorthread attached to the lower end of the elongated tail member.

To make the stent, the tail may be molded in one piece with the tubularsegment, or it may be made separately and attached to the bladder endregion of the tubular segment at a point toward the kidney from thebladder end of the lower region of the tubular segment. In one specificembodiment, the tail is attached near or at the bladder end of thebladder end region of the tubular segment. The stent may include asuture securing the tail to the tubular segment, and the suture may beincorporated into the tail to impart strength to the tail so the tailmay be used to retrieve the stent. If the tail includes a hollow lumen,the suture may be positioned inside that lumen. The suture may beattached to the tubular segment at a point in the bladder end region ofthe tubular segment, and the suture may extend from the point ofattachment through an opening in the bladder end region to the centrallumen of the tubular segment and from there to the hollow tail.Alternatively, at least the bladder end region of the tubular segmentmay include two lumens, a main urine-transporting lumen and a bladderlumen to encase the suture, so that the suture does not becomeencrusted.

The outer diameter of the tubular segment can be tapered so that itdecreases approaching its lower region. The lower region of the tubularsegment may include multiple openings positioned, e.g., axially alonginclude its length or radially around its circumference, or in otherpatterns. In addition, the outer diameter of the stent's tubular segmentmay decrease approaching the upper region. In other words, the maximumdiameter may be at the site of the injury to encourage a sufficientlylarge inner diameter in the repaired structure, and the tubularsegment's outer diameter may decrease moving away from that point ofmaximum diameter to sections of the normal ureter that are not in needof a broad support structure. Typically, the outer diameter of the upperend of the tubular segment will be greater than the outer diameter ofthe bladder end. The upper region may include multiple openings(inlets).

In an alternative embodiment, the elongated external urine-transportsurface is a continuous surface extending from the kidney to thebladder, e.g., it is the outer surface of a solid member extending fromthe kidney to the bladder.

Another aspect of the invention features a method of introducing aureteral stent (described above) into a patient, by (a) positioning thekidney end region of the tubular segment within the renal pelvis; and(b) positioning the elongated flexible member(s) in the bladder.

Yet another aspect of the invention features a method of manufacturing aureteral stent as described above. The method comprises: (a) providing apolymer pre-form having a tubular shape; (b) forming an elongatedtubular stent segment from the polymer pre-form, and (c) providing tailmember(s) at an end region of the tubular segment designed to bepositioned toward the patient's bladder.

As described in greater detail below, the stent may be manufactured froma polymer form having a tubular shape by forcing the form onto a mandrelto produce the desired three dimensional shape (coils, etc.). Theelongated tubular member(s) is attached to one end of the tubularmember(s) using sutures as described above. Heat treatments to fuse thestructures and/or standard adhesives may be used. Alternatively, thetubular member(s) and the elongated member constitute a one-piece stent.

The use of relatively thin, flexible elongated member(s) to assist urineflow across the ureterovesical junction and into the bladder may reducereflux and irritation and thereby reduce patient discomfort and medicalproblems associated with ureteral stents.

Other features and advantages of the invention will appear from thefollowing description of the preferred embodiment, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a ureteral stent with a central portion of thetubular segment omitted.

FIG. 2 is a cross-sectional view along line 2—2 in FIG. 1.

FIG. 3 is an enlarged side-view of a portion of the ureteral stent inFIG. 1.

FIG. 4A is a view of an alternate embodiment of the stent in FIG. 1, andFIG. 4B is a section taken along 4B—4B of FIG. 4A.

FIGS. 5A and 5B are schematic representations of another stent accordingto the invention, depicted in place.

FIGS. 6A-6D depict alternative cross-sections of the tail of a stentaccording to FIG. 5.

FIG. 7 is a schematic representation of yet another stent according tothe invention, having an extraction thread.

FIG. 7A is an enlargement of a portion of FIG. 7.

FIG. 8 is a schematic representation of the stent of FIG. 7 shown inposition.

FIG. 8A is a detail of the connection between the tail and theextraction thread.

FIG. 8B is a cross-section of threads of differing softness, showing theeffect of compression on interstitial space.

FIG. 9 shows an alternative embodiment of the stent.

FIG. 10 is a schematic drawing of the human urinary tract without astent, showing the renal pelvis, the kidney, the ureter, and theureteral orifices opening into the bladder.

FIG. 11 depicts a prior art double-J stent outside the body.

FIG. 12 depicts a prior art J indwelling ureteral stent in position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, ureteral stent 100 includes an elongated tubular body 130connecting coil end 140 to straight end region 120. Tubular body 130 isdesigned to extend from the renal pelvis through the ureter to aterminus upstream of the bladder. Tail 110 is attached to straight endregion 120, and tail 110 extends along the ureter, across theureter/bladder junction and into the bladder.

The two opposing end regions 120 and 140 of elongated tubular body 130are illustrated in FIG. 1. Coiled end region 140 is designed to beplaced in the renal pelvis of the kidney. For illustrative purposes,coiled end region 140 is shown with a pigtail helical coil although anyshape that will retain the stent in place within the kidney will do.Coiled end region 140 includes several openings 125 placed along thewall of the tubular body; the openings may be arranged in variousgeometries (e.g., axial, circumferential, spiral). The entire tubularsegment, including the region between the kidney and the bladder endregions, may include additional openings.

The bladder end region 120 of the tubular stent segment is designed toterminate in the ureter, upstream of the bladder. For purposes offurther description, the end region of stent 100 received in the kidneywill be designated the kidney end and the opposite end of stent 100toward the bladder will be termed the bladder end.

FIG. 2 is a cross-sectional view of stent 100 of FIG. 1. In FIG. 2,elongated tubular body 130 has annular walls 250 having an inner andouter diameter. The outer diameter of tubular body 130 may besubstantially uniform throughout much of the length of the tube, or itmay taper from a relatively short region of larger diameter (the site ofthe repair, where there is a risk that the healing process willsubstantially restrict flow in the lumen) to a region of generally smalldiameter. The precise configuration may depend on the ureteral defectbeing corrected. Just one of the many classes of procedures that canbenefit from the stent are endopyelotomies—procedures for treatingureteropelvic junction (UPJ) obstruction by an incision which perforatesthe ureter at the stricture. In these and other procedures, the stentkeeps the ureter lumen open during the healing process, so that theinner diameter of the resulting healed structure is adequate. Thesection of the tubular segment at the defect is large enough to supportgrowth of repair tissue having an adequate inner diameter. At othersections of the ureter (e.g., sections not being surgically repaired),the outer diameter of the tubular segment may be far smaller, but withan inner diameter adequate for passage over a guidewire. For example,the outer diameter of the bladder end region of the tubular segmenttypically is 2Fr.-12Fr. Preferably the outer diameter of tubular body130 is greatest at the ureteropelvic junction obstruction but begins totaper approaching each end. Alternatively, for a patient with an upperureteral obstruction, the upper (kidney) portion of the tubular member130 may be uniform in diameter, tapering just in the lower (bladder)portion.

Tubular member 130 defines a central lumen or passageway 260, extendingfrom kidney end region 140 to bladder end region 120. The inner diameterof lumen 260 is sufficient to permit passage over a guidewire. Tubularbody 130 may also have openings 125 extending through its walls 250 tofacilitate the flow of urine from the kidney into central lumen 260 andopenings 127 to facilitate flow out of central lumen 260.

In FIG. 3, the outer diameter of elongated tubular body 130 tapers nearbladder end region 120. The outer diameter of bladder end region 120 maybe made as small as possible while maintaining the ability to pass overa guidewire. Elongated tubular body 130 may (but need not be)substantially straight in bladder end region 120, i.e. it does not coilor curve in the absence of external force. When tail 110 is a singlefilament, it typically is thinner than even the smallest portion ofbladder end region 120 of the tubular stent segment. Alternatively, itmay be desirable to design the tail from multiple filaments, each ofwhich, by itself, is much thinner than the bladder end region of thetubular stent segment. Together, such a multi-filament tail has a largereffective diameter, providing additional bulk while maintaining comfort.Tail 110 may be attached at or near the end of region 120, and itextends from that attachment into the bladder. Tail 110 is either solidor hollow. It can be generally cylindrical in shape; alternatively, itcan be fluted, concave (quarter-moon)-shaped or it may assume othershapes.

The tail can have an outer diameter that is significantly less than theinner diameter of the ureter (typically 2-5 mm) and no greater than theouter diameter of the tubular segment from which it extends. For examplethe tail diameter is less than 10Fr. and as low as a suture (about0.5Fr). Preferably the tail diameter is between 2Fr. and 4Fr. The lengthof tail 110 is preferably between 1 and 100 cm. In one embodiment, thetail is long enough so that at least a portion of it will remain in thebladder, and effectively the entire tail cannot migrate up into theureter. Preferably the length is between 1 and 40 cm. Tail 110 isflexible and, upon application of force, can be curved, but also hasmemory such that when the force is removed, it is generally straight.

Stent 100, including tail 110 and tube 130, may be a single unit. Thus,tail 110 can be a unified piece, extending from bladder end region 120with no additional attachment means. Alternatively tail 110 can besecured to elongated tube 130 or bladder end region 120 by physical ormechanical methods.

For example, in FIG. 4A, a suture 415 is inserted through an opening 418in the tubular member and then threaded through the lumen 417 of tubularmember 430. In FIG. 4B, tail 410 is a hollow member having suture 415threaded through its inner lumen 412.

FIG. 5 is a schematic of another stent 510. The kidney end A of thestent has a pre-formed memory bend, to coil 512 as shown. Kidney end Ais larger and more rectangular to help prevent upward as well asdownward stent migration. End A may be closed or tapered to accommodatevarious insertion techniques. For the upper portion (A—B) of the stent,diameter, lumen size, perforations and materials are conventional. Thelower end 514 of the tubular stent segment ends at B. The distance A—Bcould vary depending on the patient's anatomy. At B, the stent istapered (or at least smooth and constant in diameter).

Two or more monofilament or coated (plastic or silicone) threads 516exit from the lumen or from the stent wall. These threads only partiallyfill the ureter and are as flexible (soft) as possible. Typically, theyare cut to a length which forces confinement within the bladder.

The portion of the upper segment 512 lying within the renal pelvis (e.g,from the kidney end of the stent to point A) is expanded so that it islarger in section, and it may even be oval or rectangular incross-section, to help prevent upward as well as downward stentmigration. The kidney end of the stent may be closed and/or tapered toaccommodate the desired insertion technique. The upper portion 512 ismade of a relatively stiff material (among the materials currently usedin ureteral stents), and it should be designed to effectively restrictthe motion of the stent to prevent proximal as well as distal migrationof the catheter during normal physiological activity (required becausethe lower pre-formed portion is deleted). The length of the straightportion of the upper segment (FIG. 5A point A to B) will vary withpatient size and anatomy. In the preferred configuration, the uppersegment extends more than halfway down the ureter when in properposition. The lowest end of the upper segment (FIG. 5A point B) shouldbe tapered or beveled to facilitate withdrawal. Otherwise, the uppersegment is a typical stent in diameter, materials and shape.

The lower segment (FIG. 5A point B to point C) consists of two or more(e.g four) monofilament, plastic coated or silicone coated threads(shown in section in FIG. 5B) which extend from the lumen or sidewall ofthe lower end of the upper segment (FIG. 5A point B) along ureter 513into the bladder. These threads are extremely flexible, and theirdiameter is selected to maintain a passage for urine flow and yetdrastically reduce bladder and ureteral irritation. By avoidingdistortion of the ureter wall, the threads may inhibit urinary reflux aswell. The threads should be long enough to reach well into the bladder(FIG. 5A point C), but not so long as to wash into the urethra withvoiding. One thread 518 (or two or more threads in a loop) may be longenough to exit through the urethra (FIG. 5A point B to point D) topermit ready removal by pulling (avoiding cystoendoscopy).

These extended threads may also be used for stent exchange, in which asecond catheter is exchanged for the catheter already in place.According to that procedure, these extended threads are captured with asnare that has been inserted through the central lumen of a secondcatheter. The snare is used to pull the threads through the lumen as thesecond catheter is advanced into the ureter. A guidewire is theninserted through the central lumen of the second catheter to the kidney(outside the first catheter's tubular body). The first stent is thenremoved by pulling on the threads, leaving the guidewire in position forplacement of a new stent using standard techniques.

FIGS. 6A-6D are alternative cross sectional sketches (taken at the samelocation as FIG. 5B) of some possible arrays of threads passing withinthe lower ureter 517. Multiple threads 516 (2 and 4, respectively) areshown in FIGS. 6A and 6B. A substantially similar conduit could beachieved by fluted type cross sections in a single filament FIGS. 6C and6D). The shapes of FIGS. 6C and 6D could also be effective in reducingstiffness and hence irritability at the bladder end (i.e., lowersegment), e.g., in a single filament design. Multiple threads may havethe advantage of better surgical manipulability and superior comfort tothe patient.

Further refinements are described below and in FIGS. 7 and 7A which dealwith: a) proximal or upward stent migration of either the entire stentor individual threads in the lower segment independent of upper segmentmovement; b) bunching of one or more threads within the ureter so as toobstruct flow or cause ureteral injury or knotting at the time ofremoval; and c) in multi-thread embodiments, discomfort and/or reduceddrainage through the ureter resulting from the use of threads ofdifferent lengths. In FIGS. 7, 6 F (F=French size=circumference in mm)stent is a generally a good size for adult urinary systems. It is largeenough to provide good drainage and small enough to minimize localirritation and inflammation of the ureter. In this embodiment, the uppersegment need be only a single loop of conventional size because a changein the design of the lower segment (see later discussion and FIG. 8)should prevent proximal migration. The upper segment (FIG. 7 point A topoint C) is constructed of a relatively firm material because, duringinsertion, the pusher tubing should be removed after the guidewire isremoved. This means that there will be some drag on the threads duringremoval of the pusher tubing which could dislodge the stent if the coil(FIG. 7 point A to point B, about 2.5 cm) does not provide adequateresistance. The coil may be tapered or closed depending on the insertiontechnique desired (i.e., over a previously placed guidewire.

FIG. 7 point B to point C should have an approximate length of 12 cm.This is long enough to prevent dislocation of the upper segment in alarge renal pelvis and short enough to end well above the point wherethe ureter crosses the common iliac vessels. At the iliac vessels, theureter takes a fairly sharp turn and the threads will more easily followthe natural curves at this point. This design should reduce theinflammation that is normally seen in this region when a conventionaldouble-J stent is left indwelling on a chronic basis.

The junction of the upper and lower segments at FIG. 7 point C isimportant. See FIG. 7A, which enlarges this junction. At point C (FIG.7) the threads are attached to the upper segment in a manner thatachieves the following goals: 1) the threads are securely attached tothe upper segment and to each other (at least for a short distance ofabout 0.8 mm) so that their orientation to themselves is maintained (tothe maintenance of lower end asymmetry); 2) the threads do not obstructthe lumen of the upper segment and they allow for the easy passage of astandard guidewire (e.g., 0.035 guidewire); 3) the transition diametersin this region closely preserve the 6F standard so that this point canpass in both directions smoothly throughout the instruments used forinsertion and through the ureter; 4) there is no cause for a localizedureteral obstruction; and 5) there is an effective abutment for thepusher tubing. For an average size ureter a good starting stringdiameter for a four string lower segment (FIG. 7 point C to point E)would be 0.020 inches. A simple monofilament nylon thread is an easypotential solution but may be too stiff. A more supple monofilament orwoven thread with silicone or other coating may be required to achieveminimal irritability. However, the threads should be sufficientlyresistant to compression so that tissue generated pressures cannotcollapse the interspaces of the threads. See FIG. 8B, showingcross-sections of threads (left) which retain interstitial space undersome modest compression and of threads (right) which are so soft thatthey compress into a plug with reduced interstitial space. These threadsmay have centimeter markings beginning at a point no more than 20centimeters from point B (FIG. 7) so that functional ureteral and totalstent length may be noted.

The portion of the lower segment which lies within the bladder when thestent is in proper anatomic position (FIG. 7 point D to point E) isimportant to, both comfort and function. Proximal migration can becontrolled by using asymmetrical lengths of the thread pairs, with onepair being 2 cm longer than the other pair, so that the fused junction810 of these threads tends to intersect with the ureteral orifice 814 atan angle (e.g., ˜90°) with the stiffened area 815 having a length of 6mm (see detail FIG. 8A). In the ideally fitted stent of this embodiment,the thread pairs will extend beyond the ureteral orifice (FIG. 7 pointD) by 1 cm at the short limb 820 and 3 cm at the long limb 825. However,this lower segment configuration allows for considerable tolerance insizing (unlike unsecured independent threads which must be selected tohave a length so as to avoid upward migration of the thread through theureteral orifice 814) and a chosen length which is 1 cm shorter or 2-3cm longer than the ideal length should be satisfactory. Using thisconfiguration the threads should form a continuous loop 828 of 3.5 cmlength to prevent free ends from poking the bladder wall or prolapsingthrough the urethra. Buoyant threads may add to patient comfort, becausethey will float away from the trigone region of the bladder, where mostof the sensory nerve fibers are located. A typical small gauge filamentextraction thread 830 may be attached to the longer limb 825 of thethread pairs, which is a suitable pulling point for removal.

From this embodiment, a small diameter pusher tubing of 4-4.5F should beused to aid insertion. Soft percuflex is near optimal for the lowersegment, and firm or regular percuflex is used for the upper segment.

The bladder end should be easily inserted using instruments, and itshould prevent proximal migration of the stent. The design of FIG. 7will avoid tangling and migration of the stent. Alternatively, softpercuflex, for example, has good resistance to extreme flexion at smallradii (e.g., even 0.020″ diameter) so that a simple continuous loopextending from the junction of the upper and lower segments (see FIG. 9)may be adequate to prevent upward migration. The design of FIG. 9 alsohas the advantage of relative ease of manufacture and relative ease ofinsertion, as well as ease and comfort of removal.

Other dimensions that can be used (without limitation) are 12 cmstraight portion of the upper hollow shaft, and 12 cm, 14 cm, or 16 cmlength of added loops of soft percuflex. For the 0.020″ diametermaterial, either 2 or 3 loops may be used providing 4 or 6 strings,total. For 0.040″ inch material, either 1 or 2 loops is recommended.

FIG. 9 shows such an alternative embodiment having a simple coil at thekidney end. The lower end is constructed of looped stringlike elementswith ends fused at the junction between the lower and the upper end.Therefore, there are an even number of string elements, with no freeends. Circle E in FIG. 9 represents an idealized depiction of theureteral opening into the bladder. While not shown in FIG. 9, the loopsmay be fused over a very short distance at the bladder end in order toprevent tangling of loops and to improve stent handling. Anyconventional means of fusion may be used. Optionally, organization ofthe loops can be maintained by pre-placing them inside the pusher tubingusing a long monofilament nylon loop tail, similar to those used for thenon-invasive removal stents (i.e. without sensor endoscopy).

Methods for insertion and removal of ureteral stents are known in theart. Generally, stent placement is achieved by advancing the tubularstent segment over a guidewire in the ureter. A pushing catheter passesthe tubular segment into the kidney, while maintaining the tail in thebladder. Other methods such as a stiff sheath can be used to positionthe stent. Once in position, the sheath can be removed.

The tubular portion of the stent may be manufactured by extruding a tubeaccording to known techniques. The elongated tail may be separatelymanufactured by conventional techniques and attached to the tubularportion, e.g., using biocompatible adhesive materials or heat.Alternatively, the stent may be made by injection molding the tube andthe tail as a single piece, using a pin to create hollow segments. Thestent may be manufactured from any of a number of biocompatible polymerscommonly used inside the body, including polyurethane and polyethylene.In still other embodiments, the entire stent may be solid, so that urineis conveyed entirely on an external stent surface.

1. A ureteral stent for assisting flow of urine, the stent comprising:i. an elongated tubular segment extending from an upper region includingat least a first opening to a lower region having an external surfaceand including at least a second opening, the lower region having alength sufficient to be positioned in a ureter when the ureteral stentis in use, and defining a lumen extending therethrough connecting thefirst opening to the second opening; ii. a coiled end region extendingdistally from the upper region of the tubular segment to be positionedsubstantially in a kidney when the ureteral stent is in use; and iii. athin flexible elongated tail having an external urine-transport surface,the thin flexible tail being substantially straight and tapering to asmaller outer diameter as it transitions from the lower region of thetubular segment so as to receive urine from the lower region of thetubular segment and to transport the urine along the urine-transportsurface, and including a transition from the external surface of thelower region of the tubular segment to the urine-transport surface ofthe thin flexible tail that is continuous.
 2. The stent of claim 1 inwhich the external urine-transport surface when the ureteral stent is inuse extends along at least part of the ureter, across the ureter/bladderjunction, and from there through the ureteral opening into the bladder.3. The stent of claim 1 in which the thin flexible tail is solid.
 4. Thestent of claim 1 in which at least part of the tail is hollow.
 5. Thestent of claim 1 in which the tubular segment includes multiple openingsalong its length.
 6. The stent of claim 1 wherein the externalurine-transport surface of the tail is continuous and uninterrupted. 7.A ureteral stent for assisting flow of urine, the stent comprising: i.an elongated tubular segment extending from an upper region including atleast a first opening to a lower region having an external surface andincluding at least a second opening, the lower region configured toextend more than halfway down a ureter when the ureteral stent ispositioned in the ureter, and defining a lumen extending therethroughconnecting the first opening to the second opening; ii. a coiled endregion extending distally from the upper region of the tubular segmentto be positioned substantially in a kidney when the ureteral stent is inuse; and iii. a thin flexible elongated tail having an externalurine-transport surface, the thin flexible tail being substantiallystraight and tapering to a smaller outer diameter as it transitions fromthe lower region of the tubular segment so as to receive urine from thelower region of the tubular segment and to transport the urine along theurine-transport surface, and including a transition from the externalsurface of the lower region of the tubular segment to theurine-transport surface of the thin flexible tail that is continuous. 8.The stent of claim 7 in which the external urine-transport surface whenthe ureteral stent is in use extends along at least part of the ureter,across the ureter/bladder junction, and from there through the ureteralopening into the bladder.
 9. The stent of claim 7 in which the thinflexible tail is solid.
 10. The stent of claim 7 in which at least partof the tail is hollow.
 11. The stent of claim 7 wherein the externalurine-transport surface of the tail is continuous and uninterrupted.